1. Field of the Invention
The invention relates to a drawing pen exchanging device, for computer controlled drawing machines, wherein at least one spring holding element holds the drawing pen in a receptacle in the drawing head, along with at least one stationary drawing pen magazine. The drawing pen is held with the aid of at least one spring-pressure element such that the drawing pen can be exchanged by engaging the receptacle and the drawing pen magazine between said receptacle and magazine in a straight line movement, essentially perpendicular to the longitudinal axis of the drawing pen.
2. Brief Description of the Prior Art
In the case of a known drawing pen exchanging device of this type (DE-OS 29 13 690, U.S. Pat. No. 4,288,798) the drawing pen is held in the receptacle of the drawing head by two opposing leaf springs, whose ends reach around the drawing pen slightly and press it against a stationary surface of the receptacle opposite the delivery opening. Moreover, the free ends of the leaf springs extend slightly ahead in the direction of transfer of the drawing pens to the drawing pen magazine. Two correspondingly formed springs are located in the drawing pen magazine.
When the pen is held in the drawing pen magazine and the drawing head draws near the drawing pen magazine, the free ends of the drawing head springs are located at less distance from one another (due to the fact that one drawing pen is missing), than the ends of the drawing pen magazine springs which are forced apart by the inserted drawing pen. Thusly, bringing the free ends of the drawing head springs in contact with the outer surface of the drawing pen forces them apart, as the drawing head continues to approach the drawing pen magazine. In this condition, they touch the protruding ends of the springs of the drawing pen magazine and push themselves between these springs and the drawing pen until their free ends surround the drawing pen and draw it out of the drawing pen magazine as the movement of the drawing head is reversed.
When a drawing pen is placed from the drawing head into the drawing pen magazine, the springs function in the same manner as described above, however, in this case the springs of the drawing pen magazine push themselves between the drawing head springs and the drawing pen.
Although this prior art drawing pen exchanging device operates relatively simply and also reliably, it has the disadvantage that the position of the drawing pen in the drawing head is not exactly defined, since it essentially is determined by characteristics of the two springs which can change during use. Thus, it can occur that when a drawing pen with a given line width is exchanged for a drawing pen with another line width and an attempt then is made to continue the line drawn by the first drawing pen with this new drawing pen, the newly drawn line width does not line up exactly with the existing line segment.
In the case of another known drawing pen exchanging device (DE-OS 27 55 586, U.S. Pat. No. 4,135,245) the drawing head has a retaining clamp which operates by spring force and with which the drawing pen is held to the drawing head. However, in order to transfer the drawing pen from the drawing head into a drawing pen magazine, the drawing head must first move in a straight line to the drawing pen magazine and thereby move the drawing pen into the area of the magazine. Thereupon, there is a vertical movement which transports the drawing pen within the area of the magazine into its repository and releases it from the drawing head. Then the drawing head is moved in a straight line movement parallel to the aforesaid straight line movement out of the area of the drawing pen magazine. Thus, with this second prior art drawing pen exchange assembly there necessarily is a relatively complicated movement to transport a drawing pen from the drawing head into the drawing pen magazine and vice versa.
The object of the invention is to create a drawing pen exchanging device for computer controlled drawing devices which makes it possible to exchange a drawing pen between the drawing head and the drawing pen magazine through a simple straight-line movement, whereby the drawing pen is held in a defined position in the drawing head.